AGRICULTURAL  EXPERIMENT  STATION 

BENJ.  IDE   WHEELER,  President 

COLLEGE    OF    AGRICULTURE  thomas  forsyth  hunt,  dean  and  director 

H.  E.  VAN    NORMAN,  Vice-Director  and  DEAN 
University  Farm  School 


UNIVERSITY  OF  CALIFORNIA 

IE    OF   AGRIC 

BERKELEY 


CIRCULAR  No.  107. 

October,  1913. 

SPRAYING  WALNUT  TREES  FOR  BLIGHT  AND 
APHIS  CONTROL. 

By  Ralph  E.  Smith. 
Assisted  by  T.  Francis  Hunt  and  W.  H.  Nixon. 

There  are  many  orchards  of  thrifty,  large  seedling  walnut  trees  in 
the  State,  particularly  in  Santa  Barbara,  Ventura,  Los  Angeles,  and 
Orange  counties,  which  would  be  much  more  profitable  than  at  present 
were  it  not  for  the  attacks  of  walnut  blight  and  aphis.  The  develop- 
ment of  new  walnut  varieties  more  resistant  to  blight  presents  no  relief 
to  the  owners  of  these  groves,  since  most  of  their  best  walnut  land  is 
already  occupied  by  large  trees,  and  these  trees,  moreover,  are  of  a  good 
commercial  type  and  would  yield  very  good  returns  save  for  these  two 
pests.  The  only  apparently  feasible  means  of  combating  blight  and 
aphis  on  such  trees  lies  in  the  development  of  some  practical  spraying 
method. 

The  necessity  of  controlling  aphis  as  well  as  blight  is  apparent  to 
every  walnut  grower,  since  this  pest  has  in  recent  years  become  really 
more  serious  than  the  much  dreaded  blight.  Spraying  experiments  car- 
ried on  by  this  Division  several  years  ago  seemed  to  show  the  impracti- 
cability of  controlling  blight  by  sprajdng,  on  account  of  the  time  and 
expense  required  for  treating  such  large  trees  by  ordinary  spray 
methods.  Recent  developments,  however,  in  sprayers  and  nozzles  have 
made  it  possible  .to  spray  large  trees  more  quickly  and  cheaply  than 
could  be  done  a  few  years  ago,  and  we  therefore  decided  last  year  to 
try  out  again  the  possibilities  in  this  direction.  In  this  connection  a 
considerable  acreage  of  walnut  trees  was  sprayed,  using  various  methods 
and  mixtures.  As  a  result  of  the  work,  it  may  be  said  in  brief  that  one 
method  gave  particularly  promising  results,  especially  in  the  control  of 
the  aphis.  This  method  consisted  in  spraying  the  trees,  while  they  were 
in  a  dormant  condition,  with  lime-sulphur  solution. 

Effect  on  Blight. 

The  results  of  the  spraying  upon  the  walnut  blight  were  difficult  to 
establish  on  account  of  the  slight  occurrence  of  the  disease  in  the 
sprayed  districts  during  the  past  season.     In  this  respect  the  work  was 


—  2  — 

inconclusive,  although  there  appeared  to  be  at  least  some  blight  control 
by  the  lime-sulphur  spraying.  It  is  further  to  be  said  that  there  is 
some  experience  to  indicate  that  continued  spraying  with  the  lime- 
sulphur  for  two  or  three  seasons  gradually  decreases  the  amount  of 
blight. 

Effect  on  Aphis. 

Walnut  aphis  has  in  recent  years  become  a  worse  pest  than  blight  in 
many  of  the  most  important  districts.  This  insect  spreads  the  blight 
and  multiplies  its  infections  by  carrying  the  germ  as  it  crawls  about  the 
trees.  Further,  it  reduces  the  vitality  of  the  tree,  checks  its  growth, 
reduces  the  size  and  weight  of  the  nuts  and  contributes  to  the  occurrence 
of  "perforation,"  "stick-tights"  and  other  conditions  which  decrease 
the  crop  and  increase  the  cost  of  handling  the  nuts.  The  effect  upon 
aphis  of  spraying  trees  with  lime-sulphur  during  the  winter  time  has 
been  well  marked  in  our  work  during  the  past  season.  Well  sprayed 
trees  remained  comparatively  free  of  aphis  long  after  the  insect  had 
become  abundant  on  unsprayed  trees.  The  nuts  of  sprayed  trees  were 
larger  and  cleaner,  the  foliage  cleaner  and  more  vigorous  looking  and  the 
growth  of  the  trees  continued  later  in  the  season.  The  spraying  was 
done  in  each  case  upon  a  few  rows  surrounded  by  unsprayed  trees  and 
from  the  latter  the  aphis  finally  spread  to  some  extent  to  the  trees  which 
were  sprayed.  It  is  reasonable  to  expect  that  if  whole  orchards  had 
been  treated  the  aphis  control  obtained  would  have  been  still  better. 
The  results  of  these  experiments  were  so  promising  that  we  feel  justified 
in  carrying  the  work  farther  and  urging  growers  to  take  up  the  work  on 
their  own  account  during  the  coming  season. 

Formula. 

Our  best  work  was  done  with  the  following  mixture : 

Commercial  lime-sulphur  solution 5  gallons 

Quick  lime 25  pounds 

Water 95  gallons 

The  lime  is  slaked,  strained  and  then  added  to  the  mixture.  So  far 
as  we  know  the  addition  of  the  lime  is  not  necessary  to  the  effect  of  the 
spray,  but  this  was  added  in  order  to  make  it  easier  to  see  it  upon  the 
trees.  The  trees  are  usually  large  and  without  the  addition  of  lime  it  is 
very  difficult,  especially  for  inexperienced  workmen,  to  cover  the  trees 
thoroughly  without  missing  more  or  less  of  the  twigs  and  branches. 

Time  of  Spraying. 

The  work  was  intended  to  be  done  while  the  trees  were  in  a  dormant 
condition,  i.  e.,  during  the  months  of  February  and  March.  The  solu- 
tion burned  the  foliage  severely  if  any  leaves  were  out  when  the  work 
was  done,  but  it  is  possible  that  the  aphis  is  more  susceptible  at  this 
time. 


—  3  — 

Outfit. 

In  order  to  spray  by  this  method,  a  power  outfit  must  be  used  which 
will  maintain  a  constant  pressure  with  two  lines  of  hose  of  200  to  250 
pounds.  A  pressure  of  200  pounds  at  the  very  least  is  necessary  in 
order  to  cover  the  tops  of  tall  trees  thoroughly  by  this  method. 

In  regard  to  nozzles,  our  best  results  were  obtained  by  spraying  the 
trees  with  the  so-called  M.  A.  C.  nozzle — a  special  nozzle  made  in  the 
East  for  this  sort  of  work.  Some  preferred  using  an  outfit  with  two 
lines  of  hose,  one  man  spraying  the  upper  part  of  the  trees  with  this 
nozzle  while  the  other  sprayed  the  lower  parts  with  an  ordinary  Bor- 
deaux or  Cyclone  type  of  nozzle.  The  largest  walnut  trees  can  be 
spra}red  entirely  from  the  ground  by  the  use  of  the  M.  A.  C.  nozzle  if 
the  proper  pressure  is  maintained. 

Method. 

The  whole  success  of  the  work  depends  upon  thoroughly  coating  the 
trees  out  to  the  tips  of  the  smallest  twigs  with  the  spray  solution.  This, 
with  large  walnut  trees,  is  a  somewhat  difficult  and  laborious  task  and 
also  an  expensive  one.  By  using  the  type  of  nozzle  suggested,  how- 
ever, and  working  with  intelligence  toward  covering  all  the  growth 
quickly  and  at  the  same  time  thoroughly,  workmen  can  acquire  much 
skill  in  this  respect  and  the  work  can  be  done  economically  enough  to 
more  than  justify  its  expense.  Herein,  however,  lies  the  whole  secret 
of  the  operation :  that  is,  spraying  rapidly  and  yet  thoroughly. 

Amount  of  Material  Required. 

In  our  work  last  winter  the  amount  of  material  used  varied  in  differ- 
ent places  from  25  to  67  gallons  per  tree.  These  were  trees  of  varying 
size,  but  it  is  still  to  be  considered  that  as  the  work  progressed  and  the 
workmen  became  more  experienced,  it  became  possible  to  spray  larger 
trees  with  a  smaller  amount  of  material  and  at  the  same  time  do  the 
work  even  more  thoroughly.  It  may  be  said  upon  this  point  that  about 
25  gallons  of  spray  to  a  tree  will  be  required  to  cover  fair  to  middle- 
sized  walnut  trees  thoroughly — that  is,  trees  of  average  size  up  to  about 
ten  years  of  age — while  large  trees  will  average  about  40  gallons  per 
tree. 

Time  Required. 

With  a  power  sprayer  having  three  men  on  the  outfit  and  another  to 
mix,  or  seven  men  to  two  outfits,  we  averaged  about  85  large  trees  per 
day  to  each  outfit.  In  one  case  an  average  of  110  fair  sized  trees  per  day 
was  made,  while  in  another  case  40  per  day  was  averaged  for  trees  of  the 
very  largest  size.  The  time  required  varies  naturally  with  the  facilities 
for  loading  up.  In  our  work  the  spray  outfit  went  after  its  load  each 
time  to  the  mixing  station  and  the  distance  thus  covered  varied  in  dif- 
ferent places.  A  little  time  could  be  saved  profitably  in  extensive  work 
by  hauling  or  piping  the  mixture  out  to  the  spray  rig  in  the  orchard. 


—  4  — 

Expense. 

Materials  were  purchased  at  a  price  of  $10  per  50  gallon  barrel  of 
commercial  lime-sulphur  solution,  and  $1.10  per  hundredweight  for 
lime.  On  this  basis  the  spray  in  the  proportion  recommended  above 
cost  $.01275  per  gallon.  The  expense  of  application  was  estimated  on 
the  following  basis  for  each  power  outfit : 

Per  day. 

Four  men  at  $2.00  each , $8  00 

Two  horses  at  $1.00  each 2  00 

Depreciation    of    outfit 2  00 

Oil   and   gasoline 1  00 

Total    $13  00 

On  this  basis  the  expense  of  application  per  gallon  varied  from  $.004 
to  $.007.  Assuming  an  average  expense  of  application  at  $.00525  and 
that  for  material  at  $.01275,  we  get  a  total  expense  of  $.018  per  gallon  on 
the  tree.  At  this  rate,  25  gallons  per  tree  would  cost  $.45,  while  40 
gallons  would  cost  $.72  per  tree,  total  expense  of  material  and 
application. 

Consideration  of  Expense. 

It  will  be  seen  that  the  cost  of  this  work  is  by  no  means  prohibitive  if 
even  a  moderate  degree  of  blight  and  aphis  control  be  obtained.  It  is 
also  to  be  considered  that  beneficial  effects  would  almost  certainly  be 
cumulative,  so  that  after  spraying  trees  for  two,  or  at  most  three,  suc- 
cessive seasons  the  work  could  very  probably  be  discontinued  for  a  year 
or  two  without  throwing  the  trees  back  into  as  bad  condition  as  they 
were  in  the  beginning. 

Furthermore,  it  is  altogether  probable  that  the  cost  estimated  above 
could  be  reduced  to  a  considerable  extent  by  carrying  on  systematic  work 
on  a  large  scale.  In  the  expense  for  material  and  labor  the  cost  of  the 
commercial  lime-sulphur  solution  amounts  to  an  average  of  about  55  per 
cent  of  the  total  cost.  The  labor  item  averages  about  30  per  cent  of  the 
total  and  the  lime  makes  up  the  remaining  15  per  cent.  It  is  probable 
that  the  lime  could  be  omitted  altogether  when  the  workmen  became 
skilful  enough  to  spray  the  trees  thoroughly  without  such  an  indicator 
to  make  the  material  more  easily  seen;  this,  so  far  as  we  know,  is  the 
only  object  of  using  the  lime.  The  lime-sulphur  solution  is  estimated 
at  the  prevailing  retail  price  and  it  is  possible  that  by  buying  in  large 
quantities  (for  instance,  through  walnut  associations),  a  better  rate 
could  be  obtained.  It  is  also  possible  that  the  associations  or  even  the 
growers  could  prepare  the  materials  themselves  at  a  lesser  cost  than  that 
estimated.  The  labor  item  will  be  reduced  as  the  workmen  become  more 
skilful  and  could  also  be  lessened  to  some  extent,  at  least  in  large  work, 
by  arranging  to  deliver  the  material  to  the  spraying  outfits  in  the 
orchard  more  rapidly  than  was  done  in  our  experiments.     Two  ex- 


—  5  — 

perienced  men  could  spray  and  run  the  outfit,  rather  than  the  three 
which  we  have  estimated.  One  man  could  also  mix  the  spray  for  a 
number  of  outfits.  The  amount  of  material  used  per  tree  can  also 
be  reduced  somewhat  as  the  workmen  become  more  experienced. 
Altogether,  it  appears  to  us  possible  that  the  expense  of  spraying  trees 
of  average  large  size  by  this  method  may  be  ultimately  reduced  to  about 
fifty  cents  per  tree.  We  do  not,  however,  look  for  much  further  reduc- 
tion than  this,  unless  some  much  cheaper  spray  material  is  found  to  be 
effective.  The  work  can  not  be  done  properly  without  using  compara- 
tively large  amounts  of  time  and  material.  At  $.50  per  tree,  a  very 
moderate  degree  of  success  in  aphis  control  alone  would  be  a  most 
profitable  investment  in  the  increased  growth  of  the  tree  and  yield  of 
nuts,  as  well  as  the  improvement  in  quality  and  reduction  in  cost  of 
handling  the  nuts. 

Further  Work. 

We  recommend  to  large  growers  and  associations  especially  that  work 
along  this  line  be  taken  up  during  the  coming  season,  in  order  to  test 
more  fully  the  value  of  this  spraying.  We  recommend  that  entire 
orchards  or  blocks  of  trees  be  sprayed,  in  order  that  a  more  complete 
test  may  be  obtained  than  that  which  results  from  spraying  a  few  trees 
or  rows  in  the  midst  of  other  unsprayed  trees.  We  do  not  guarantee 
spectacular  results  from  such  work,  but  do  believe  that  if  it  is  done 
thoroughly  the  effect  will  more  than  justify  the  expense.  On  the  part 
of  the  University  we  expect  to  continue  experimental  spraying  another 
season,  testing  some  other  promising  materials,  and  will  also  agree  to 
furnish  co-operation  to  all  who  undertake  the  work  to  the  extent  of 
general  oversight,  information  and  suggestions.  We  should  also  be  glad 
to  take  up  the  matter  of  the  purchase  of  apparatus  with  all  who  con- 
template walnut  spraying,  in  order  that  they  may  obtain  the  right  sort 
of  appliances  and  have  them  in  ample  season. 

ILLUSTRATIVE    RESULTS. 

Bishop  Ranch,  Goleta:    Very  large,  old  trees.     March  26-30,  1913. 
Formula. 

5  gallons  Ortho  lime-sulphur  solution,  25  pounds  lime,   to  100  gallons  of 
spray  mixture. 

Quantity. 

11,600  gallons  applied  to  173  trees. 
Labor. 

4^  days  at  $13.00 $58  50 

3  spray  men  at  $2.00 $6  00 

1  mixer  at  $2.00 2  00 

2  horses  at  $1.00 2  00 

Depreciation   of  outfit 2  00 

Oil   and   gasoline 1  00 

Total $13  00 

Labor  =  $.005  per  gallon. 


—  6  — 

Material. 

580  gallons  lime-sulphur  at  $.20 _  $110  00 

2,900  pounds  lime  at  $1.10 31  90 

$147  90 

Material    $.01275  per  gallon 

Labor     .005       per  gallon 

Total    $.01775  per  gallon 

Total  Amount  Applied. 

67  gallons  per  tree  =  $1.19,  total  expense  per  tree. 
Expense   Summary. 

Labor $58  50  =  281  per  cent 

Lime-sulphur    116  00  =  56^  per  cent 

Lime 31  90  =  15     per  cent 

RESULTS. 

This  work  was  done  with  extreme  thoroughness  and  some  wasting  of 
material.  The  trees  were  some  of  the  largest  in  the  State,  however,  and 
very  difficult  to  cover  thoroughly.  Not  enough  blight  developed  during 
the  following  season  to  afford  definite  indications  as  to  blight  control  by 
the  spraying.  The  effect  upon  aphis  was  well  marked,  the  sprayed  trees 
being  noticeably  free  from  this  pest  quite  late  in  the  season.  The 
foliage  on  trees  which  were  partly  in  leaf  at  the  time  of  the  spraying  was 
badly  burned  by  the  solution. 

Robert   Main    Ranch,  Goleta:    Medium  sized  trees.      March  31-April   1,  1913. 
Formula. 

5   gallons  Ortho  lime-sulphur  solution,   25   pounds  lime,   to  100  gallons  of 
spray  mixture. 
Quantity. 

4,800  gallons  applied  to  165  trees. 
Labor. 

U  days  at  $13.00 $19  50 

3  spray  men  at  $2.00 $6  00 

1  mixer  at  $2.00 2  00 

2  horses  at   $1.00 2  00 

Depreciation   of  outfit 2  00 

Oil   and   gasoline 1  00 

Total $13  00 

Labor  =  $.00406  per  gallon. 
Material. 

240  gallons  lime-sulphur  solution  at  $.20 $48  00 

1,200  pounds  lime  at  $1.10 13  20 

$61  20 

Material     $.01275  per  gallon 

Labor     .00406  per  gallon 

Total    $.01681  per  gallon 

Total  Amount  Applied. 

29  gallons  per  tree  =  $.48749,  total  expense  per  tree. 
Expense  Summary. 

Labor $19  50  =  24*  per  cent 

Lime-sulphur 48  00  =  59i  per  cent 

Lime 13  20  =  16     per  cent 


—  7  — 

RESULTS. 

The  foliage  on  these  trees  was  considerably  advanced  when  the  spray- 
ing was  done  and  the  leaves  and  yonng  shoots  were  badly  burned,  so  that 
a  large  amount  of  the  new  growth  fell  off.  Another  growth  developed 
on  the  trees,  but  the  crop  was  considerably  cut  down  by  this  injury. 
The  effect  on  aphis  control  was  excellent,  the  sprayed  trees  being 
noticeably  clean  late  in  the  summer,  the  nuts  and  leaves  larger  and 
the  growth  of  the  trees  more  vigorous  later  in  the  season.  There 
appeared  to  be  rather  less  blight  on  the  sprayed  than  on  unsprayed 
trees,  but  the  disease  was  not  abundant  enough  to  warrant  positive 
conclusions. 

Limoneira    Ranch,  Santa   Paula:    Medium   large  trees.     April  2-4,   1913. 
Formula. 

5  gallons  Ortho  lime-sulphur  solution,  25  pounds  lime,   to  100  gallons  of 
spray  mixture. 

Quantity. 

o.OOO  gallons  applied  to  200  trees. 

Labor. 

(2  outfits). 

1%  days  at  $24.00 $36  00 

6  spray  men  at  $2.00 $12  00 

1  mixer  at  $2.00 2  00 

4  horses  at  $1.00 4  00 

Depreciation  of  outfits 4  00 

Oil  and  gasoline 2  00 

Total $24  00 

Labor  =  $.0072  per  gallon. 

Material. 

250  gallons  lime-sulphur  at  $.20 $50  00 

1.250  pounds  lime  at  $1.10 13  75 

$63  75 

Material     $.01275  per  gallon 

Labor .0072     per  gallon 

Total $.01995     per  gallon 

Total  Amount  Applied. 

25  gallons  per  tree  =  $.50,  total  expense  per  tree. 

Expense   Summary. 

Labor $36  00  =  36  per  cent 

Lime-sulphur    50  00  —  50  per  cent 

Lime 13  75  =  14  per  cent 

RESULTS. 

These  trees  were  scarcely  in  leaf  when  the  spraying  was  done  and  con- 
sequently no  serious  burning  resulted.  The  sprayed  trees  were  notice- 
ably more  free  from  aphis  than  the  unsprayed  quite  late  in  the  season. 
The  leaves  and  the  nuts  were  cleaner  and  somewhat  larger  and  more 
thrifty.  The  trees  also  seemed  to  maintain  their  growth  later  in  the 
season.  This  grove  was  situated  upon  heavy  land,  with  irrigation,  and 
did  not  develop  as  much  aphis  upon  unsprayed  trees  as  in  most  cases. 


SUMMARY. 

Aphis  and  blight  are  the  two  most  serious  pests  of  the  English  walnut. 
In  the  experiments  described  in  this  circular  very  promising  results  in 
the  control  of  aphis  were  obtained  and  there  is  reason  to  believe  that 
blight  may  be  controlled,  to  some  extent  at  least,  by  the  same  means. 

The  best  results  were  obtained  by  spraying  the  trees  while  in  a  dor- 
mant condition  (or  just  as  the  first  growth  was  starting),  with  lime- 
sulphur  solution.  The  proportion  used  consisted  of  5  gallons  of  com- 
mercial lime-sulphur  to  95  gallons  of  water.  Twenty-five  pounds  of 
quicklime,  slaked  and  strained,  was  also  added,  to  make  the  spray 
more  visible  upon  the  trees. 

The  problem  of  spraying  such  large  trees  quickly  and  economically 
was  met  by  the  use  of  high  power  sprayers  and  a  special  nozzle  (the 
so-called  M.  A.  C),  making  it  possible  to  cover  the  largest  trees  com- 
pletely from  the  ground. 

The  essential  thing  for  success  in  this  work  is  to  cover  the  trees  abso- 
lutely with  the  spray,  from  the  trunks  to  the  tips  of  all  the  twigs. 

The  amount  of  material  required  for  spraying  good  sized  trees 
thoroughly  averaged  from  30  to  50  gallons  per  tree. 

The  average  cost  of  material  was  $.01275  per  gallon ;  that  for  labor  and 
other  expenses  of  application  $.0055  per  gallon;  the  average  total  cost 
per  tree  being  about  $.55.  This  may  probably  be  reduced  to  $.50  per 
tree  for  average  large  trees,  by  having  experienced  workmen  and  buying 
or  making  the  spray  material  in  large  quantities. 

An  average  of  85  large  trees  per  day  was  sprayed  by  one  outfit  with 
four  men  (or  seven  men  to  two  outfits) . 

The  results  obtained,  while  not  accurately  measurable  the  first  year  in 
pounds  of  walnuts,  seemed  to  more  than  justify  the  cost  in  improved 
condition  and  increased  growth  of  the  trees,  nuts  and  foliage. 


